1. Field of the Invention
The present invention specifically relates to a drive device using a small, lightweight electromechanical conversion element and is applied to drive an optical element or the like in an optical device.
2. Description of the Related Art
Under conditions where a camera is unsteadily held while taking a photograph, image blurring occurs in the imaging plane. A well known means to correct this phenomenon includes an optical stabilization system in which two corrective lenses, positioned immediately behind the aperture of the photographic lens are driven eccentrically within the plane, perpendicular to the optical axis. In a lens device equipped with such an optical stabilization system, the lens device incorporates a special drive mechanism which drives the corrective lenses in a given direction.
A conventional drive mechanism, comprising a direct current motor and a gear reduction mechanism, is one example of the aforementioned mechanism which drives the corrective lenses in an optical stabilization system. Such a design, however, not only entails a large motor, but also occupies a large amount of space since the gear reduction mechanism also incorporates a mechanism to eliminate backlash. Consequently, the lens barrel is unavoidably large. Also, the noise produced during the operation when the gear reduction mechanism is operated, is an additional inconvenience detracting from the quality of its operation.
The present invention heretofore provides a corrective lens drive mechanism having a drive source of an actuator using a piezoelectric element (see Japanese Laid-Open Patent Application No. 8-43872).
As shown in FIG. 17, the aforementioned, conventional, corrective lens drive mechanism has a drive source of an actuator using a piezoelectric element. A first actuator 122 eccentrically moves a first lens group L1 parallel to the X-axis direction, and a second actuator 123 eccentrically moves a second lens group L2 parallel to the Y-axis direction.
The first actuator 122 and second actuator 123 have an identical design and include a piezoelectric element 132 (142), drive shaft 131 (141) and friction-linked connector 112a (113a). The first and second actuators form an integrated structure comprising a lens retaining frame 112 (113), pad 112c (113c), and plate spring 112d (113d) which adjusts the frictional linkage force.
An X-axis position sensor 135 is attached to the lens retaining frame 112 which detects the X-axis position of the first lens group L1. A Y-axis position sensor 145 is attached to the lens retaining frame 113 which detects the Y-axis position of the second lens group L2. The X-axis position sensor 135 and Y-axis position sensor 145 may be of the conventional type. For example, a magnetic field resistance-type sensor 135 (145), which is attached to the lens retaining frame 112 (113), detects the magnetic field of a magnetic rod 136 (146) positioned parallel to the drive axis 131 (141), at a given distance, in the extension of a lens barrel (not illustrated).
The drive of the first lens group L1 by the first actuator 122 and second lens group L2 by the second actuator 123 are described hereinafter with reference to FIG. 17.
The amount by which a corrective lens should be driven is calculated based on the position of the lens as detected by the aforementioned position sensors, and the amount of camera shake detected by the output of a camera shake sensor (not illustrated). For example, a camera shake sensor which detects acceleration of the camera along the X-axis and the Y-axis. A drive pulse based on the calculated amount of the drive is then applied to the piezoelectric element of an actuator, and the corrective lens is then driven.
The drive pulse, as illustrated in FIG. 18, having a wave form of a moderately rising component followed by a rapidly falling component, is applied to a piezoelectric element 132 of actuator 122. As the moderately rising component of the drive pulse piezoelectric element 132 gradually generates an expansionary displacement in the direction of its thickness, the drive shaft 131 is displaced in the direction indicated by arrow a. Thus, the lens retaining frame 112, frictionally linked to drive shaft 131 by connector 112a, also moves in the direction of arrow a, and the first lens group L1 is displaced along the X-axis in the direction indicated by arrow a.
At the rapidly falling component of the drive pulse, the piezoelectric element 132 rapidly generates a contractionary displacement in the direction of its thickness, and the drive shaft 131 is also displaced in the direction opposite that indicated by arrow a. At such time, the lens retaining frame 112, frictionally linked to the drive shaft 131 by connector 112a, is overcome by the frictional linkage force with the drive shaft 131 due to its penetrating force, and because the lens retaining frame 112 is essentially stopped in that position, the first lens group L1 does not move.
By continually applying drive pulses of the above-noted wave form to the piezoelectric element 132, the first lens group L1 can be continually moved in the positive direction of the X-axis.
The first lens group L1 can be moved in the negative direction of the X-axis, i.e., the direction opposite that of arrow a, by applying to the piezoelectric element 132 a drive pulse having a wave form with a rapidly rising component followed by a moderately falling component.
The drive of the second lens group L2 by its actuator 123 is identical to the first lens group L1, and by applying a drive pulse to its piezoelectric element 142 of the actuator 123, the second lens group L2 can be displaced in the direction of the Y-axis (positive or negative direction), indicated by arrow b.
The above-described actuator using a piezoelectric element does not occupy a large amount of space. Therefore, the overall device can be made smaller and lighter than a drive mechanism comprising a direct current motor and gear reduction mechanism. Such an actuator is also equipped for superior performance inasmuch as noise is not generated during its operation. However, the use of two corrective lenses makes the design complex. Thus, a device having fewer number of parts, which is smaller and easier to manufacture, has long been sought after.
For this purpose, consideration has been given to reducing the number of parts and lowering the weight by creating molded structural parts from a synthetic resin. It has been learned, however, that when an actuator using a piezoelectric element employs such items molded from a synthetic resin, the oscillation of the piezoelectric element cannot be adequately converted to drive power, due to the elastic deformation of such molded items.